Here is Paul Foster’s translation of the passage (2010), altered to take into account Mark Goodacre’s conjectural emendation of “cross” to “Crucified One”:
[10.38] Then those soldiers seeing it awoke the centurion and the elders, for they were present also keeping guard.  While they were reporting what they had seen, again they saw coming out from the tomb three men, and the two were supporting the one, and a Crucified One following them.  And the head of the two reached as far as heaven, but that of the one being led by them surpassed the heavens.  And they were hearing a voice from the heavens saying, “Have you preached to those who sleep?”  And a response was heard from the Crucified One, “Yes”.
Once the infamous “walking, talking cross” is removed from the text – by Mark’s quite convincing emendation – the text is still a little unusual. For the Crucified One (Jesus) and his two companions, on departing from the tomb, have become giants. And that is, on most accounts, a quite unusual feature. Jesus’ two companions are so tall that their heads touch heaven. But Jesus is even taller, an even bigger Giant. For Jesus’ head surpasses the heavens, implicitly entering into the very throne room of God, where Christ’s head is questioned by the voice of God, and makes a succinct, one-word answer to God in return. The conversation is even overheard on Earth, implicitly by the Roman centurion, guards, and Jewish elders.
From very early times, at least by the first century AD, it was a reasonably common idea that heavenly messengers, or angels, and even Jesus and Christians, had to change their bodily form in order to ascend into the heavens. In the Gospel of John (20.19, 26), the legendary resurrected Jesus walks through locked or shut doors, and in the Gospels of John (20.14) and Luke (24.16), Jesus’ own disciples do not recognise him after he has transformed into a resurrection body. In the second century Christian work, the Acts of Peter (21), different witnesses see Jesus in different forms, even at a single post-resurrection appearance: some see him as an old man, some see him as a young man, some see him as a young boy.
But while the transformation of the post-resurrection Jesus into various forms is not unusual in these early Christian legends, his transformation into a Giant who reaches all the way from Earth into the highest heaven is rather more unusual. How did the Gospel of Peter arrive at such a novel transformation … or giganticization? In the first place, we might note that the Gospel of Peter was, as far as we know, the first gospel to provide a narrative of the resurrection of Jesus. In the earlier extant Gospels, we only get stories of the aftermath of the resurrection. So, there are stories about already emptied tombs, post-resurrection appearances, zombie saints moving about in Jerusalem, etc. What this probably means is that the Gospel of Peter could not rely on any established tradition of the precise mechanics of the resurrection and had to compose his own.
I propose that the author of the Gospel of Peter utilised Old Testament scripture to fill this gap. To wit, he employed LXX Psalm 18 (MT Psalm 19) as the basis of his new resurrection narrative. The LXX translates the Hebrew כגבור (“like a hero/mighty man/man”) as ὡς γίγας (“like a Giant”).
That’s a brief outline of my argument, which I might write up more formally for publication. I haven’t read enough to work out if this has all been suggested before, and haven’t examined variants, let alone much of the secondary literature on the Gospel of Peter. But, in the meantime, I very much welcome comments, questions, and suggestions.